Especially for reducing costs for photovoltaic cells, research is done all around the world for finding a solid state composition of creating an interpenetrating solid-state conducting material in a nanoporous network. Such device could also be used for LED (Light Emitting Diodes), photo sensors, optical switches and even optical networks.
The present invention relates to a photo device comprising a layer of nanometer sized particles and a conducting polymer in solid state, wherein the nanometer sized particles are chosen from the group of TiO2, ZnO, CdSe, CdS, ZrO2 and SnO2, and wherein the conducting polymer comprises PPV (polyparaphenylenevinylene) or a derivative thereof.
Prior methods have been published on the insertion of a polymer electrolyte into a preformed nanocrystalline TiO2 (titanium dioxide) network (F. Cao et al., Proceedings of Nanostructured Materials in Electrochemistry, held: Reno, Nev., USA, 21-26 May 1995). These methods have, however, the disadvantage of being based on an ionic conductor. The device performance is therefore limited. The ionic conductor is not suited for electronic devices.
Another prior method using conducting polymers (PPV and derivatives) replaces the inorganic nanocrystalline network with C60 and derivatives which act as electron-acceptors (G. Yu et al., Science 270 (1995) 1789). However, in this method, the electron transport is restricted. Further, C60 is not a material which is produced abundantly, and is expensive; it is also much less stable than inorganic materials.
Another prior method using a conjugated polymer, poly(2-methoxy, 5-(2xe2x80x2-ethyl)-hexyloxy-p-phenylenevinylene; MEH-PPV), incorporates nanoparticles of CdS or CdSe (N. C. Greenham et al., Physical Review B. Condensed Matter, 54 (1996) 17628, N. C. Greenham et al., Synthetic Metals 84 (1997) 545-546), but the cadmium-containing compounds have a disadvantage in that they are carcinogenic and also not abundantly available.
Another publication (S. A. Carter et al., Applied Physics Letters 71 (1997) 1145) discloses the use of TiO2 nano-particles blended with electroluminescent organic material in light emitting diodes. As an example, MEH-PPV was tested as organic material. The mixtures were spin cast onto an Ito coated glass, whereafter the solvent was evaporated off. The device lacks photovoltaic properties.
The present invention has for its object to offer a solution to the problem of creating an interpenetrating solid-state conducting material in a nanoporous network, for the purpose of creating stable, all-solid state photovoltaic cells. The instability problems associated with liquid based electrolytes in nanoporous networks (B. O""Regan et al., Nature, 353 (1991) p737) are to be avoided.
A further object of the present invention is to offer a photovoltaic cell, which offers the stability, electron transporting properties, the abundant availability, the low costs, and the no-toxicity of TiO2 in an interconnected network in combination with the hole-transporting, light-absorbing, stable properties of PPV (poly-paraphenylenevinylene).
A further aspect of the present invention is the ease of manufacturing, namely in a single thermal treatment of the inorganic and organic materials together. The thermal treatment is elegantly simple, and provides for converting the polymer precursor to its final, conducting form as well, as for producing electrical contact between the inorganic nanometer sized particles to make continuous electron-carrying pathways to the end terminal of the photovoltaic cell, the object of the present invention.
None of the above prior art methods use a mixture of a polymer precursor in solution and inorganic nanometer sized particles in a colloidal solution to produce an interpenetrating composite layer in a single step of thermal treatment.
A preferred embodiment of the method according to the present invention uses a conducting polymer precursor (poly(p-xylene-alpha-tetrahydrothiophene-bromide; p-PPV) and a nanocrystalline material, TiO2.
Another preferred embodiment of the method of the present invention is that the mixture of PPV precursor or derivative there of and TiO2 is between 10:90 and 70:30 by weight, preferably approximately 50:50.